Dual-Source Lighting: A Bright Idea

Taking a walk around the modern workplace illuminates a verifiable truth: Lighting affects the way we work. The best solution for building occupants (as well as the budget) often leaves ergonomists, facilities managers, and CFOs scratching their heads.

Using just one source of overhead or ambient lighting for the entire office (single-source lighting) may seem like the more budgetary choice, but it doesn’t provide occupants with any control over the lighting levels at their workstations, and is inadequate at illumination for detailed tasks, such as reading and writing. Task lighting is ideal for detailed work, but it’s inadequate for illuminating the overall workspace.

Further complicating matters is the fact that people need different lighting levels depending on their age, vision strength, and job tasks. For example, since paper reflects light, reading paper-based documents requires up to five times more light than viewing a monitor. This presents an obvious conflict for most office environments, where employees are reviewing both paper and digital material.

A possible answer to this quandary is dual-source lighting. This lighting method uses low levels of ambient/overhead lighting in combination with task lights at each workstation. It’s a solution that provides ergonomic, economic, and environmental benefits.

Ergonomically, dual-source lighting provides controllable lighting for people with varying vision levels, which has been shown to increase productivity.

Environmentally, dual-source lighting can reduce the amount of energy wasted by excess ambient lighting. Using dual-source lighting can even help organizations earn LEED credits.

Putting Dual-Source to the Test

The question that most organizations’ decision-makers want an answer to is: How big of a difference can dual-source lighting really make? A landmark study conducted by Duke University and North Carolina State University, which assessed the benefits of adjustable LED task lighting on posture and comfort, put dual-source lighting to the test.

The study involved the voluntary participation of 100 clinical researchers at a major U.S. medical center. As compensation for their involvement, the participants received an adjustable LED task light to keep. Using a random-placement, control/intervention experiment design, the study provided the intervention group with an adjustable LED task light for use in the study. Prior to receiving the task light, intervention and control group participants completed questionnaires about discomfort, eye fatigue, and perceived control over their jobs.

After the task lights were given out, researchers adjusted the overall lighting levels for the intervention participants; after several days, researchers asked all participants to complete online surveys similar to the first questionnaire they took. Intervention group participants also answered questions about task light usability. At the end of the study, their compliance with using task lighting was observed.

The study revealed that a combination of reduced overhead lighting and adjustable task lighting can positively impact posture and perceived well-being. In particular, the intervention group rated their discomfort levels with their right shoulders, right upper arms, and right wrists as being reduced. The intervention group also reported a reduction in the frequency and interference of discomfort within all upper-body areas, especially the neck and right upper arm.

But will employees really use an adjustable LED task light if they have one? The researchers’ observations revealed a post-study task light compliance of 87.8 percent among intervention group participants, indicating that employees saw a benefit to continuing to use the task light after the study was complete. Intervention group participants also overwhelmingly agreed that the task light helped with performance and visual fatigue; participants also expressed a strong desire to have the lights in their workspaces.

As more research is developed, support continues to grow for the rapidly emerging theory that dual-source lighting helps elevate an organization’s bottom line and transforms it into a more comfortable, accommodating place to work.

Mary Michael Townsend

Mary Michael Townsend is a freelance writer with years of experience as a seating and ergonomics specialist within the contract furniture industry. She can be reached at marymichaelt@gmail.com.